derive_more_impl/
deref_mut.rs

1use crate::utils::{
2    add_extra_where_clauses, numbered_vars, panic_one_field, SingleFieldData, State,
3};
4use proc_macro2::TokenStream;
5use quote::quote;
6use syn::{parse::Result, Data, DeriveInput};
7
8/// Provides the hook to expand `#[derive(DerefMut)]` into an implementation of `DerefMut`
9pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
10    match input.data {
11        Data::Struct(_) => expand_struct(input, trait_name),
12        Data::Enum(_) => expand_enum(input, trait_name),
13        _ => panic!("only structs and enums can use `derive({trait_name})`"),
14    }
15}
16
17fn expand_enum(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
18    let state =
19        State::with_field_ignore_and_forward(input, trait_name, "deref_mut".into())?;
20
21    let trait_path = &state.trait_path;
22    let enum_name = &input.ident;
23
24    let mut match_arms = vec![];
25    let mut predicates = vec![];
26
27    for variant_state in state.enabled_variant_data().variant_states.into_iter() {
28        let data = variant_state.enabled_fields_data();
29        if data.fields.len() != 1 {
30            panic_one_field(variant_state.trait_name, &variant_state.trait_attr);
31        };
32
33        let vars = numbered_vars(variant_state.fields.len(), "");
34        let matcher = data.matcher(&data.field_indexes, &vars);
35
36        let info = data.infos[0].clone();
37        let field_type = data.field_types[0];
38
39        let var = if info.forward {
40            let casted_trait = data.casted_traits[0].clone();
41            predicates.push(quote! { #field_type: #trait_path });
42            quote! { #casted_trait::deref_mut(__0) }
43        } else {
44            quote! { __0 }
45        };
46
47        match_arms.push(quote! {
48            #matcher => #var
49        });
50    }
51
52    let generics = if predicates.is_empty() {
53        &input.generics
54    } else {
55        &add_extra_where_clauses(&input.generics, quote! { where #(#predicates),* })
56    };
57
58    let (imp_generics, type_generics, where_clause) = generics.split_for_impl();
59
60    Ok(quote! {
61        #[allow(deprecated)] // omit warnings on deprecated fields/variants
62        #[allow(unreachable_code)] // omit warnings for `!` and other unreachable types
63        #[automatically_derived]
64        impl #imp_generics #trait_path for #enum_name #type_generics #where_clause {
65            #[inline]
66            fn deref_mut(&mut self) -> &mut Self::Target {
67                match self {
68                    #(#match_arms),*
69                }
70            }
71        }
72    })
73}
74
75fn expand_struct(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
76    let state =
77        State::with_field_ignore_and_forward(input, trait_name, "deref_mut".into())?;
78    let SingleFieldData {
79        input_type,
80        trait_path,
81        casted_trait,
82        ty_generics,
83        field_type,
84        member,
85        info,
86        ..
87    } = state.assert_single_enabled_field();
88    let (body, generics) = if info.forward {
89        (
90            quote! { #casted_trait::deref_mut(&mut #member) },
91            add_extra_where_clauses(
92                &input.generics,
93                quote! {
94                    where #field_type: #trait_path
95                },
96            ),
97        )
98    } else {
99        (quote! { &mut #member }, input.generics.clone())
100    };
101    let (impl_generics, _, where_clause) = generics.split_for_impl();
102
103    Ok(quote! {
104        #[allow(deprecated)] // omit warnings on deprecated fields/variants
105        #[allow(unreachable_code)] // omit warnings for `!` and other unreachable types
106        #[automatically_derived]
107        impl #impl_generics #trait_path for #input_type #ty_generics #where_clause {
108            #[inline]
109            fn deref_mut(&mut self) -> &mut Self::Target {
110                #body
111            }
112        }
113    })
114}
derive_more_impl/deref_mut.rs

derive_more_impl/
deref_mut.rs
